1. Field of the Invention
The present invention relates to a following device, and in particular to a following device which automatically follows a moving object with shooting direction of a camera caused to move automatically.
2. Description of the Related Art
A following device is a device which causes a pan head on which a television camera is mounted to pan/tilt with motor drive so as to automatically move the shooting direction of a camera and automatically follow moving subjects. As a method of following, the one described in Japanese Patent Application Publication No. 59-208983 is widely known. According to this method, an image covering two frames (covering two screens) in a predetermined time span from image signals outputted from a camera, and an image of a moving object is extracted with comparison of those images. In addition, from the position of the center of gravity of that extracted moving object, moving amount as well as moving direction of the moving object is detected, and the shooting direction of the camera is automatically controlled with panning/tilting of the pan head so that the center of gravity of the moving object always stays in the center of the screen based hereon.
In the present specification, operations of the pan head caused to move the shooting direction of the camera in the panning direction or the tilting direction will be referred to as the panning direction or tilting direction of the pan head or merely the movement of the pan head.
In the method of following described in the above described Japanese Patent Application Publication No. 59-208983, in order to extract images of a moving object by comparing images covering two frames taken in from a camera, the pan head is required to halt while those images for comparison are being taken in. That is, difference in shooting ranges of images for comparison due to movement of the pan head gives rise to movement of the image of the static objects on the screen so as to make it impossible to distinguish the image of the moving object and therefore the pan head cannot be moved while the images for comparison are being taken in. Thus, the above described following method cannot follow moving objects which move fast, and the pan head repeats movement and halt, giving rise to such defaults that the screen becomes less vision-friendly.
Under the circumstances, in order to overcome such a defect, the present applicant of the present application has proposed in Japanese Patent Application Publication No. 2000-175101 a method of following which has made it possible to extract the image of the moving object also from images of different shooting ranges and to recognize the images of the moving objects in spite that the pan head is being moved. According hereto, in spite that the pan head is halted or is moving, the images are taken in from the camera and the pan/tilt position of the pan head at that time is acquired. When images covering two frames are taken in a predetermined time, based on the pan/tilt position when each image is taken in, the shooting range of the camera at the time when each image was shot is given and the overlapping range in the shooting range of each image is determined as the comparison range. Within this comparison range, since the image of a static object does not move, comparison of images in the comparisons range will enable extraction of images only of the moving object.
However, the method of following in Japanese Patent Application Publication No. 2000-175101 detects the position of the moving object on the screen so as to control panning/tilting of the pan head so that its position will come approximately to the center of the screen, and thus the pan head will move following the movement of the moving object. Accordingly, when the moving velocity of the moving object gets fast, under such control of the pan head, the moving object would get out of the shooting range of the camera, and might result in failure to follow. In addition, since the moving velocity of the moving object cannot be determine, smooth following is unattainable.
In addition, in the method of following described in the above described Japanese Patent Application Publication No. 59-208983, a slight movement of the moving object within the shooting range of the camera results in a movement of the pan head and a movement of the shooting direction of the camera. Thus, due to defects such as swings of the screen and poor visualization of a camera, the applicant of the present application has provided a range of dead zone in the central portion of the screen in U.S. patent application Ser. No. 09/726,496 and has proposed such a method of following that is caused not to move the pan head in the case where a moving object is moving within the range of that dead zone.
However, the method of following of U.S. patent application Ser. No. 09/726,496 also has problems to be improved. For example, the moving velocity of a moving object could be naturally fast and could be slow, and in the case where the moving velocity is slow, no such events that movement of the pan head gets out of the screen will take place when the moving object gets out of the range of dead zone but in the case where the moving velocity is fast, the moving object gets out of the screen and following could become no longer executable.
Moreover, for example, when the moving object comes inside the screen from outside the shooting range (screen) of the camera, the moving object moves toward the center of the screen (the center of the horizontal direction or the perpendicular direction of the screen) and when a static object inside the screen starts moving, that moving object could move toward the center of the screen. In such a case, essentially, in spite of unnecessity of moving the pan head, in the conventional method of following, following is controlled without discriminating such movement circumstances of a moving object from other moving circumstances, and therefore the pan head will start moving immediately after the movement of the moving object is detected and useless operation of following is executed, giving rise to a problem that the images of the camera will become less visible.